Systems and methods for treating high sulfate water and injecting treated water

Abstract

A method for treating water high in sulfate includes passing the water at a temperature of 10° C. to 45° C. through a nanofiltration membrane module and a reverse osmosis membrane module in series such that the retentate stream from the nanofiltration membrane module is fed to the reverse osmosis membrane module. A first permeate stream from the nanofiltration membrane module has at least 90% lower sulfate content than the feed stream. A second permeate stream from the reverse osmosis membrane module has at least 95% lower sulfate content than the retentate stream from the nanofiltration membrane module. The first and second permeate streams are combined to form a treated stream containing less than 40 ppm sulfate. A system including the nanofiltration and reverse osmosis membrane modules in series is also disclosed.

What is claimed is: 
     
         1 . A method for treating water high in sulfate, comprising:
 a. passing a feed stream of water having an initial sulfate content greater than 100 ppm at a temperature of between 10° C. and 45° C. through a nanofiltration membrane module and a reverse osmosis membrane module in series such that a first retentate stream from the nanofiltration membrane module is fed to the reverse osmosis membrane module;   b. producing a first permeate stream from the nanofiltration membrane module wherein the first permeate stream has at least 90% lower sulfate content, at least 50% lower magnesium content and at least 30% lower calcium content with respect to a sulfate, magnesium, and calcium content, respectively, in the feed stream;   c. passing the first retentate stream to the reverse osmosis membrane module to produce a second permeate stream having at least 95% lower sulfate content, at least 90% lower magnesium content and at least 90% lower calcium content with respect to a sulfate, magnesium, and calcium content, respectively, in the first retentate stream;   d. combining the first and second permeate streams to form a treated stream containing less than 40 ppm sulfate; and   e. removing a second retentate stream from the reverse osmosis membrane module as a reject stream.   
     
     
         2 . The method of  claim 1  wherein the initial sulfate content of the water is greater than 500 ppm. 
     
     
         3 . The method of  claim 1  wherein the treated stream contains less than 10 ppm sulfate. 
     
     
         4 . The method of  claim 1  wherein the percent recovery of the treated stream relative to the feed stream is greater than 50%. 
     
     
         5 . The method of  claim 1  wherein the percent recovery of the first permeate stream from the nanofiltration membrane module relative to the feed stream is less than 60%. 
     
     
         6 . The method of  claim 1  wherein the percent recovery of the second permeate stream relative to the first retentate stream is greater than 40%. 
     
     
         7 . The method of  claim 1  wherein the treated stream has a salinity up to 60% lower than an initial salinity of the feed stream. 
     
     
         8 . The method of  claim 1  wherein the feed stream of water comprises produced water associated with oil and/or gas production, flowback water associated with oil and/or gas operations, aquifer water and/or seawater. 
     
     
         9 . The method of  claim 1  wherein the method occurs on an offshore oil and/or gas production platform or vessel. 
     
     
         10 . The method of  claim 1  further comprising pretreating the water prior to step (a) such that the feed stream contains no greater than 50,000 ppm total dissolved solids, 5,000 ppm sulfate, 2,000 ppm calcium and 2,000 ppm magnesium. 
     
     
         11 . The method of  claim 1  wherein the pretreating is done by a pretreatment method selected from the group consisting of particle filtration, ultrafiltration membranes, clarifying, softening, primary, secondary and tertiary deoiling, desanding, and combinations thereof. 
     
     
         12 . The method of  claim 1  further comprising injecting the treated stream through an injection well into an oil and/or gas reservoir without treating the treated stream further prior to injection. 
     
     
         13 . The method of  claim 1  further comprising injecting the treated stream through an injection well into an oil and/or gas reservoir without the addition of a biocidal agent to any stream during the method. 
     
     
         14 . A system for treating water high in sulfate, comprising:
 a. a nanofiltration membrane module for receiving a feed stream of water having an initial sulfate content greater than 100 ppm and forming a first permeate stream and a first retentate stream;   b. a reverse osmosis membrane module located such that the first retentate stream from the nanofiltration membrane module is fed to the reverse osmosis membrane module and wherein the reverse osmosis membrane module forms a second permeate stream and a second retentate stream; and   c. a conduit in which the first permeate stream and the second permeate stream are combined to form a treated stream containing less than 40 ppm sulfate.   
     
     
         15 . The system of  claim 14  further comprising a feed pump for delivering the feed stream to the nanofiltration membrane module. 
     
     
         16 . The system of  claim 14  wherein the feed stream of water comprises produced water associated with oil and/or gas production, aquifer water and/or seawater. 
     
     
         17 . The system of  claim 14  further comprising a pretreatment module selected from the group consisting of particle filters, ultrafiltration membranes, clarifiers, softeners, primary, secondary and tertiary deoiling equipment, desanding equipment, and combinations thereof. 
     
     
         18 . The system of  claim 14  further comprising an injection well in an oil and/or gas reservoir for injecting the treated stream into the oil and/or gas reservoir. 
     
     
         19 . The system of  claim 14  wherein each of the nanofiltration membrane module and the reverse osmosis membrane module have a plurality of membrane elements. 
     
     
         20 . The system of  claim 19  wherein the reverse osmosis membrane module has a number of membrane elements that is greater than 40% of a number of membrane elements in the nanofiltration membrane module. 
     
     
         21 . The system of  claim 14  wherein the system is located on an offshore oil and/or gas production platform or vessel. 
     
     
         22 . The system of  claim 14  further comprising a booster pump located between a retentate outlet of the nanofiltration membrane module and an inlet of the reverse osmosis membrane module. 
     
     
         23 . The system of  claim 14  further comprising an energy recovery turbine or a pressure exchanger to recover energy from a reject stream from the reverse osmosis membrane module.